Suction piles, piles or caissons have been used subsea to anchor floating vessels or to form a foundation for a subsea structure. A suction pile, or suction anchor, is formed as a cylinder shaped object which is open at one end and closed at the other end, and with a system for pumping out fluid from the inside of the cylinder shaped object through the close end.
When the suction pile is installed, the open end is positioned on the seabed. Due to the weight of the structure, and by pumping out fluids through the closed end to create a suction pressure in the structure, the open end of the structure is forced, or driven, down into the seabed until a given height of the suction pile is positioned below the seabed surface. The anchor is kept in place by a combination of friction forces between the cylinder shaped wall of the suction pile and the seabed. By this, a sturdy foundation or anchoring point in the seabed is achieved. The suction pile may be used to anchor a floating vessel or as a foundation upon which may position and anchor a seabed structure, as for instance a template for a part of a subsea oil production facility. A subsea structure may be anchored to one or several suction piles. One subsea template may for instance be positioned with a suction pile in each of the four corners of the template.
Normally such suction piles are formed from a metallic material, and the subsea structures are normally welded to these suction piles or fastened to fastening means which are welded to the closed end of the suction piles. Some examples of known suction piles are described in International Publication Nos. WO 2012/062693, WO 2008/012414 and WO 2010/068119. A possible new way of forming a suction pile is to form it from a composite material, thereby reducing the weight of the suction pile structure compared to a structure made of steel. However, a subsea structure that is to be anchored and positioned on top of a suction pile is normally of a different material than composite material, making the use of standard/well known attachment system difficult, if not impossible.
There is therefore a need to provide a system for connecting or attaching a subsea structure or an anchor line for a floating vessel to a suction pile which will work if the suction pile is made of a composite material.
Another need exists to provide an attachment or connection system such that the structural strength of the suction pile, possibly made of a composite material, is maintained.
A suction pile is positioned and kept in the seabed by creating suction within the anchor; hence, there is a need to provide a suction pile with an attachment system which does not pose a risk of leakage into the interior of the suction pile.
The invention is set forth and described in independent claim 1, while other characteristics of the invention are identified in the dependent claims.